Don’t be afraid of asking for help _______ it is needed.

A．unless

B．since

C．although

D．when

预防维生素D中毒的关键措施是()

A．定期测体重

B．严密观察及时发现中毒症状

C．间断应用维生素D

D．定期测血钙

E．严格按医嘱用药